Mercury 7th May from Bangor, Co Down. 06:00 to 11:20 BST  By Dr Andy McCrea IAA President

One Terrific Transit …

My birthday month is May and my recollections for astronomical events in this month don't include a lot of sunshine and clear skies - several gloomy eclipse cloud-outs over the last couple of years loomed heavily. So hopes for a Mercury transit observation were rather small. I had set the alarm for six and sprung up right away to see a blanket of almost total cloud - my heart sank. I felt it as soon as my eyes properly opened - the skies were grey and heavy and there was no way I was going to see first and second contacts… Dispirited, I got up and stared hopefully in the general direction of where the Sun should have been.

Obviously my staring and mumbled prayers had some effect because eventually the clouds began to thin - just a bit - but enough to let the occasional, orange ray stream through - but tantalisingly, without properly exposing the Sun's disk. I had the Takahashi 78mm set up on my path and with the Baader filter in place I strained to make out Mercury - the clouds were just doing enough to prevent me seeing anything at all - but then at around 07:10BST a black spot popped into view - but it was in totally the wrong place …I quickly realised it was not Mercury, but an enormous group right in the centre of the Sun's disk.

Before too long Mercury appeared - inky black and just in the right place! I was in luck and had seen my first elusive transit! Under high magnification the circular disk could be clearly discerned and I could be convinced that it was blacker than the sunspots - but not by much. I was happy at that point to accept my lot, but over the course of the next half hour the cloud began to thin and eventually there were periods when the disk was completely un-obscured by wispy cloud. Early digital images taken through cloud resembled some of the first space probe shots of Venus or Jupiter with their cloud belts straddling the disk.

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The transit was to be a success! I snapped happily with the digital camera and was generally pleased that I was capturing the small dot making it's way across the Sun's disk. The sunspot group in the centre was surrounded with some dramatic penumbra and at the limb there was another association which was at the centre of a huge bright, faculae region. A couple of other lesser spots were evident and the whole thing was very absorbing.

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Thin cloud skittled across the disk over the next hour or so but it never blotted out the transit for more than a few minutes. By 09:15 I set off for work - as fate would have it I had a commitment which could not be avoided (assuming unemployment was not to be thrust on me prematurely!). Once in Belfast the cloud had noticeably thickened but I had another look and noted the tiny planet's progress. By 11:00BST the clouds were heavy and I could not see the closing stages well - I had not been able to observe ingress or egress and was denied an opportunity to detect the elusive 'black drop' effect - even worse I was unable to confirm Einstein's relativity theories - but I was more than satisfied - I had seen the transit and had recorded a few shots on the digital camera - one terrific transit!! I am already looking forward to the forthcoming Venus transit …

Andy McCrea


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